I found the perfect thing for your quad here
Sorry, yes I know...look how funny he thinks he is....I just couldn't resist. (And I've never personally understood some people's inclination to having matching rings/dogs/tatoo's etc....but whatever...that's my problem, not yours)
In all seriousness, something like these interlocking types
might be an option as well, with a kind of subtle symbolism...particularly if you get the sets custom made to your particular tastes. Maybe a 3 part ring, with the names of each other partner on each link for example.
Good luck in your search. Hopefully there's a local whitesmith or two that can help you realize your vision. (If there's a blacksmith guild in your area, there's a slight possibility they might know some)